1. Field of the Invention
The present invention relates to a luminaire having an optical element with a microprism structure for restricting the exit angle of light beams out of the luminaire.
2. Description of the Related Art
By means of optical elements of the kind mentioned above it is intended to be attained that the exit angle of light beams out of the luminaire is restricted, i.e. is smaller than a predetermined limit exit angle, in order to reduce dazzling for the observer. Further, such an optical element effects also a mechanical protection of the luminaire and in particular of the lamp in the interior of the luminaire.
Such an optical element is known for example from Austrian Patent AT-B403, 403. As is shown in FIG. 1, the known optical element has on its side towards the lamp of the luminaire pyramid-like profilings 2, so-called microprisms, arranged in rows and columns, which are formed as truncated pyramids starting from a plate-like core 3 and having an upper boundary surface (light entry surface) parallel to the base surface (light exit surface) of the core 3. The entire optical element 1 is completely of a glass clear or transparent material.
A further optical element of the kind mentioned in the introduction is disclosed for example in WO 97/36131. As shown in FIG. 2, the known luminaire 4 has a lamp 5, such as for example a fluorescent tube or the like, a reflector housing 6 surrounding the lamp 5, and an optical element 1. The optical element 1 is likewise of a plate-like core 3 of transparent material which on one side is occupied by microprisms 2 which with the formation of furrows 7—starting from their roots—taper, whereby the entirety of the microprism outer surfaces form the light entry surface 8. In order to ensure limiting of the exit angle of the light beams out of the optical element 1, lenses 9 are provided on the other side of the core 3 which forms the light exit surface.
With the known luminaire systems, although through the employment of the appropriately configured optical element an anti-dazzling effect is ensured for the observer, the brightness distribution of the light over the optical element is however not uniform, since in the vicinity of the lamp more light beams enter into the optical element than for example in the edge regions of the optical element. Although the lamp cannot be directly recognized through the optical element, due to the greater brightness its position can at least be sensed by the observer.
In order to attain a uniform emission of light of the illumination arrangement it is known, for example from WO 95/12782, to couple light from a lamp from the side into a light conductor element, which transports the light primarily parallel to its light exit surface. On the light exit surface of the light conductor element there is applied a microprism structure which on the one hand makes possible a coupling out of the light out of the light conductor and on the other hand restricts the exit angle of the illumination arrangement. Attention is, however, drawn to the fact that the illumination arrangement described in WO 95/12782 is a background illumination for displays or other screens and is not entirely suitable for room illumination.